
A. W. WARWICK. E. M. 

Member of the American Institute of Mining 
Engineers. 


Price 50 Cents. 


PUBLISHED BY 

The Industrial Printing and Publishing 
(Publishers of Mining Reporter) 
DENVER, 1903. 









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THE LIBRARY OF 
CONGRESS, 

Two Copiei Received 

MAR 26 1903 

Copyright Errtry 
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CLASS Ou )@fe. No, 

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COPY B,' I 



COPYRIGHT 1903 
BY 

THE INDUSTRIAL PRINTING <&. PUBLISHING CO. 


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INTRODUCTION. 


The following pages contain a reprint of a series of 
articles published in the Mining Reporter, under the caption 
of “Ore in Sight.” The publisher is responsible for the 
republication in pamphlet form. The author feels much 
diffidence in republication since the articles referred to 
were written at the short intervals allowed by pressure of 
other work. The subject is a difficult and complex one, 
and the author cannot hope to have covered the subject 
of ore valuation anything like completely. He hopes, how¬ 
ever, that this little work will be of suggestive interest to 
fellow engineers and of help to the students now passing 
through mining schools. It may be supplemented by some 
remarks upon the practical work of mine sampling. 

Denver, Jan. 22, 1903. A. W. W. 


PUBLISHER’S ANNOUNCEMENT. 

There has bee.n so much discussion as to the use of the 
term “Ove in Sight” or rather to its improper use, and Min¬ 
ing Reporter having for a long period advocated the adop¬ 
tion of other terms to indicate ore reserves and in response 
to requests from mining engineers as well as others inter¬ 
ested in legitimate mining we re.publish in this pamphlet 
the articles that have appeared in Mining Reporter during 
the past year. While we realize that the subject has not 
been fully covered in the accompanying pages, yet we feel 
that the articles are of more than passing interest and we 
will supplement the present pamphlet by a series of arti¬ 
cles upon the practical work of sampling mines. We trust 
that the booklet will be of benefit to those in whose inter¬ 
est it was undertaken and hope that lurther discussion will 
ensue. 

THE INDUSTRIAL PRINTiNG & PUBLISHING CO., 
Publishers of Mining Reporter, Denver, Colo., U. S. A. 





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.4 



ORE IN SiGHT.* 


Experience leads one to believe that the term, “Ore in 
Sight,” has been an unhappy combination of words. A 
significance has been attached to the term far beyond its 
real value. Literallv it means ore^ that can be seen, whilst 
as a matter of fact only a small portion of the ore so 
described can actuallv be looked at. measured and sampled. 
In the sampling of a mine in which a number of blocks 
of ore are opened up, possibiy not more' than a fraction of 
one per cent, of the total amount of ore can be actually 
taken as a sample. By measuring and sampling this small 
percentage, probability comes into play, and the chances are 
that by careful work and' close' attention to detail, a fair 
approximation can be made as to the value of ore opened 
up in a mine. 

The term, however, has come to oe regardea as meaning 
much more than this. Many engineers, who ought to know 
better,^ have even come to regard the term as meaning 
just what the literal construction of the word would implv, 
and the public, until recentlv, attached as much signifi¬ 
cance to the phrase as they would to the measuring and 
valuing of so much wheat The misuse of an accurate 
phrase is not any worse than the application of accurate 
language to express an inaccurate idea. 

Some years ago a verv obstinate old lumberman refused 
to believe that an engineer could really exactly tell the 
amount of ore in a mine. The engineer to whom he was 
talking combatted the lumberman’s statements, and af¬ 
firmed that a good miner could measure up and value ore 
just as accurately as a timber valuer could go ovc'r a sec¬ 
tion of land and value the trees standing on it, and the 
engineer really believed it. The lumberman was not slow 
in pointing out that the two cases were by no means paral¬ 
lel. In one case every tree could, if desired, be examined 
and measured. In the other case the' outside skin of the 
block of ore only could be seen, and its actual contents 
could not be told exactly until the ore had been broken 
down, sent to the surface, properly sampled and assayed. 
The lumberman readily admitted that a fair idea could be 
obtained as to the value of ore in a mine, but he was 


♦Mining Reporter, January 2, 1902. 




ORE^IN S[GHT. 


() 

obstinate in his opinion that the value so obtained could 
only be a me^e approximation. We must frankly admit 
that the lumberman had the best of the argument. 

The term “Ore in Sight” should be discarded, since it 
implies for more than what a competent and conseryatiye 
engineer would be willing to vouch for. “Ore in Sight,” 
as usually defined, means that three sides of an ore body 
must be exposed by the deyelopment, whilst other engi¬ 
neers demand that the ore block should be capable of 
being examined on four sides. By taking measuremenis 
and samples at regular intervals all around this block of 
ore, and arbitrarily assigning a certain weight per cubic 
foot, the examining engineer obtained a figure which is 
called the “value of ore in sight.” If we examine this value 
it must be obvious to anyone that it cannot be regarded 
as an exact figure. No man can tell how large thei bar¬ 
ren or low grade spots may be in the interior of the 
block. He cannot tell what swellings, or pinchings may 
occur between the points that he nas measured. It is per¬ 
fectly true that the estimated vame of a block of ground 
is as likely to be high as it is to be low, but in any case 
the figure he obtains can only be regarded as something 
which is close to the truth. The mere tact of calling the 
ore in sight does not maKe it any the more visual. It is 
the old process of deluding one’s self with words. 

We are strongly of the opinion that the term “Ore in 
Sight” should be abandoned, and replaced by some term 
which more, nearly represents the fact. We suggest that 
some such phrases as “Estimated Ore Reserves,” “Prob¬ 
able Pay Ore,” “Estimated Tonnage of Ore,” would more 
closely represent what the engineer really means to say, 
than the term “in sight.” For the protection of the public, 
who are not likely to know the lechnical restriction of 
the words “in sight,” some such phrases as w.e have sug¬ 
gested should by all means be adopted. 

We may also add that in our judgment engineers in 
their reports should also place a gauge upon the yalue of 
figures they may have obtained. For example, it is notori¬ 
ous that no engineer would care to guarantee any estimate 
they may make on a high grade pockety mine to within 
thirty per cent; on the other hand, the valuation of a large 
low grade and uniform deposit is much easier and the 
figures obtained are not likely to be subpect to enormous 
variations. It is not fair to the parties for whom the re¬ 
ports are made to let them form their own judgment as 
to how accurately a deposit can be yalued. Frequently 


ORE IN SIGHT. 7 

they are many miles away from the property, and even if 
they were on the ground, they do not know enough ahotit 
the subject to be capable of forming an opinion. At-any 
rate an engineer is paid for giving just such advice as we 
have indicated. Whatever engineers may think on this 
point, we feel sure that all those who have the’prosperity 
of the industry at heart must agree with us when we-say 
that the term “Ore in Sight’’ should go. 


MINE SAMPLING EXTRAORDINARY.* 


To The Editor: 

Dear Sir:—Much has been written on the subject of 
mine sampling, but the end is not yet; the subject remains 
fresh in eternal youth, ever varying with each new set of 
conditions, but never certain as to tonnage or values, until 
the ore is stoped out, crushed, weighed and sampled. It 
is at best then a mere approximation of values, and should 
be so called and described by the person making such 
examination; indeed it could not be otherwise as those who 
have read the series of articles on sampling now running 
through Mining Reporter will clearly see. If, for example, 
the ore is blocked out and accessible on four sides, 200 feet 
long by ninety deep, the very best the engineer can do is 
to correctly sample three sides, the roof of the bottom level 
and both exposed ends; the bottom of a level is difficult 
and expensive to sample, so much so that it is seldom at¬ 
tempted and is often impossible to accomplish. Where two 
sides only are exposed, the guesswork becomes still 
stronger, and where only one^ side is accessible imagina¬ 
tion has free play, and the value of a certain level as 
shown along its roof can be carried upwards to the high¬ 
est mountain peak, or at any rate to the “grass roots.” 
A case in point is a famous mine near Ouray, where, if my 
memory serves me, reserves were figured to the mountain 
top, 700 feet above a certain depth; here imagination ran 
riot and a solemn examination of a great mine became a 
roaring farce. In a late issue of Mining Reporter atten¬ 
tion was called to the sampling, “so called,” of a large 
Cripple Creek mine, and notwithstanding several differ¬ 
ences of five, ten, sixteen, twenty-one and in one case sixty- 
seven ounces of gold per ton between two portions of the 
same sample, the mean runs were taken to be the true 
value of the ore. This particular mine sampling has been 


♦Mining Reporter, January 2, 1902. 





8 


ORE: IN SIGHT. 


held up as a model by one of your contemporaries in the 
East of how things should be done. I take it as an obejct 
lesson to point the moral and adorn the tale. 

The tonnage found by this sampling and measurement 
was 53,646 at 8.26 ounces, $125 per ton, the vein avcTaging 
three and one-half feet wide (A); so far so good. The ex¬ 
aminer next informs us that this ore could not be broken 
as cleanly as in sampling, so he assumes a tonnage of 70,000 
with a value of 4.75 ounces, $95 per ton (B), but strange 
to say the thickness of the vein remains the same, three 
and one-half feet, as do also the other dimensions. Here 
then we are confronted with the unique phenomenon of 
the same space holding in one case (A) 53,646 tons, and in 
another (B) thirty per cent, more, or 70,000 tons. The feat 
of putting a quart of whisky in a pint jug is quite simple 
in comparison to this jugglery. We would note in passing 
that the figure 4.75 ounces per ton was apparently a safe 
one, as it is the mean value of the first 37,000 tons shipped 
from the mine; in other words, the average value of the 
smelting ore shipped from the mine prior to the sampling. 

After this event the first 37,000 tons shipped averaged 
but $75 per ton (C) (vide directors’ report. May 14th, 1900). 
Less than two months later (July 2d) the directors in a 
circular to the stockholders called attention to the assump¬ 
tion that estimate (B) had been increased as the result of 
fourteen months’ development to 250,000 tons of about $55 
ore, say in round numbers $14,000,000; later it was found 
that some little error had crept into this estimate. I 
merely allude to it as a point in the history of the mine. 

The output for the first fourteen months, following the 
sampling ending June 30th, 1900, amounted to 48,048 tons 
of an average gross value of say $71 per ton (D). 

Later the mine was sampled and reported on by a dis¬ 
tinguished foreign expert. He gave the total output of the 
mine from the beginning down to November 1st, 1900, 

.105,000 tons $8,250,000 

Deduct output prior to this: 

First sampling . 41,694 tons 3,837,359 

63,306 tons $4,412,641 

Showing an average value of $69.70 per ton (E). The 
ore then remaining in the mine was estimated at 120,000 
tons crude of a value of $19.16 per ton. In studying this 
discoveries were made that materially increased the ton¬ 
nage of the reserves. During thei year ending September 
30th, 1901, 148,067 tons of crude ore were extracted, which 






ORE IN SIGHT. 


9 


gave 66,199 tons of shipping ore, having a gross value of 
$2,506,862, or say $39.38 per ton (F). 

Let us now pause and sum up the sampling and esti¬ 
mate on which the mine was purchased, carrying it with 
subsequent results: 


1. The value found by assay 

and measurement. 

2. The assumed value. 

3. The first ore shipped after 

sampling . 

4. The output for fourteen 

months after sampling... 

5. The output from time of 

sampling to November, 1900 

6. The output for year ended 

September 30th, 1901. 

These results in brief are as follows: 
Output prior to November, 1900. 63,306 tons 
Output to September 30th, 1901. 66,199 tons 


Tons 






53,646 

at 

$125 

per 

ton 

(A) 

70,000 

at 

95 

per 

ton 

(B) 

37,000 

at 

75 

per 

ton 

(C) 

48,048 

at 

71 

per 

ton 

(D) 

63,306 

at 

69.70 

per 

ton 

(E) 

66,199 

at 

39.38 

per 

ton 

(F) 


<R4 A-19. fill 


Or say^ $53.38 per ton. In the face of this showing one 
would ask, what under heaven does the first sampling of 
the mine represent? The tonnage and value produced by 
stoping, the blocks assumed to be sampled are about as 
concordant with the sampling as were the originals and 
duplicate samples themselves. 

Tested on gross output the estimate on first blush 
appears very close, viz, $6,712,000, estimated against 
$6,919,503 produced, including all discoveries made in the 
extensive development of the mine. But in the first place 
ores of one ounce value were excluded from the original 
estimates, as we find from the following “in addition to the 
rich ores included in above e'Stimate, there are 10,000 tons 
of material containing one ounce of gold per ton and valued 
therefore at $20;” and again: “It is my' opinion, based on 
the facts stated, and on the general character of the mine 
as discovered in its old workings that fully $8,000,000 will 
be expected out of the ground already developed.” Turn¬ 
ing to last year’s production we find the ore as mined only 
ran $19.14, so the greater part, if not the whole of the 
$2,500,000 produced during this period is properly deduct¬ 
able from the original estimate, because its value is below 
that then thought profitable, i. e., $20 per ton. Moreover, 
my point is that the sampling is or no value, not whether 
the gross production be six, eight or fourteen million dol- 






10 


ORE IN SIGHT. 


lars. I claim that the substantial departure from the orig¬ 
inal estimate of 53,646 tons at $125 per ton shows the 
sampling to be unreliable and misleading. 

Second Period. 

The sampling and estimation by the foreign expert 
pricked the bubble. He found, as previously shown, that 
the ore in the veins had an average value of $19.16. To be 
explicit, the reserve® were estimated by him as 120,000 
tons at $19.16, which he immediately proceeds to mine and 
ship with the following results: 

Actual production.148,067 tons at $19.14 

Estimated production.120,000 tons at 19.16 

The discrepancy is due to discoveries made during the 
year increasing the ore reserve, presumably with ore of 
exactly the same value as that estimated. It should have 
been stated that the 148,067 tons crude ore produced 
66,199 tons of shipping ore, having a gross value of 
$2,506,862, which, after allowing $4 per ton for the gold 
value remaining in the rejected ore (dumps) showed the 
value of the crude ore mined during the past year to be 
$19.14 per ton, or two cents per ton lower than his esti¬ 
mate; as there are at least two variables in this computa¬ 

tion, the new ore discovered, and the dumps, the two 
cents discrepancy is properly divided between them. How¬ 
ever, I do not believe that the sampling of a Cripple Creek 
mine can be more accurately figured than twenty-five or 
thirty per cent., owing to the irregular character of the 
ore bodies and their very high grade. 

“ENGINEER.” 


[The above letter, which comes from a very careful and 
conscientious Colorado engineer, and one who has had a 
close and intimate experience with Cripple Creek ores, is 
published because it calls attention to some points relating 
to the sampling of mines. 

No truer statement was ever made than that made by 
the writer of the letter when he says at best the sampling 
of a mine is a mere approximation oi values. All are far 
too prone to accept estimates of ore in sight as being 
almost infallible. We go on record as saying that we have 
yet to see a mine in which the reported values of ore in 
sight have been exactly borne out by subsequent operations. 

Thei e is nothing extraordinarily uiixiCult in sampling a 
mine, using such sampling as a basis of determining 
whether the property will prove a financial success or not. 





ORE IN SIGHT. 


11 


blit there are insuperable difficulties in the way of so 
sampling a mine that the estimate can ue relied upon to 
within even five per cent. We may call attention to the 
fact that thei correct sampling of a mine involves the 
accuracy of at least lour different operations: 

1. The correct estimation of the weigi't of ore in place 
per cubic foot. 

2. The validity of the assumption that the average of 
the assays on three sides of a block of ore is the average 
of the contents of the whole block. 

3. The correct allowance for barren or low grade spots. 

4. The correctness of the assays. 

We may say a few words on each of these headings. 
The correct estimation of the weight of ore in place per 
cubic foot is something that no engineer would care to 
guarantee within ten per cent. We may say that the 
practice of calling a cubic foot of quartz in place as 140 
pounds, or say fourteen cubic feet to the ton, or a body of 
mixed galena and iron pyrites as being eight cubic feet to 
the ton, etc., are mere approximations, and how it is pos¬ 
sible for an engineer who uses these approximations to 
estimate the amount of ore in sight at a mine to within one 
per cent, is not clear to us. We may point out that a few 
years ago a South African mining engineer kept careful 
statistics of the output of a given stope, and found that the 
figures used in that country for estimating ore in sight 
was wrong by at least thirty per cent. 

The assumption that the average of the assays on three 
sides of a block of ore represents the value of the whole 
block is one that is open to question. We will take a small 
block of ore, which we will say is 150 feet in length and 
100 feet in depth, which can be passed around on four 
sides; we will suppose that the samples are obtained at 
regular intervals, and that in going down the sides we 
find there is an appreciable difference between the value 
of the ore at the top of the block and at the bottom. There 
is no means of telling the exact contour between the high 
grade ore and the low grade ore. By taking the average of 
the assays, this line would be perfectly straight, but there 
is just as likely to be more low grade ore in the middle 
as that the line is as assumed. Of course, it is true that 
this may balance in different blocks of ore in a mine, but 
it must be obvious that any figures obtained in this way 
are mere approximations and not absolute values. 

So far as the taking of the sample is concerned, there 
is nothing difficult about this; it simply requires a certain 


12 


ORE IN SIGHT. 


amount of hard work and a conscientious performance of 
duty. Four samples a day is about as much as one man 
unaided can take, yet we have seen engineers take as 
many as twenty-five or thirty and rely upon them in esti¬ 
mating ore in sight. 

An allusion may be made as to the influence of faults, 
horses or low grade patches. An examining engineer who 
can see through a block of ore, and accurately estimate 
such influences, could make more money as a prophet than 
as an examining engineer. An engineer must rely upon 
his experience and his judgment in this matter. This fact 
again militates against any figures as to ore in sight being 
anything more than approximation. 

We thus see that the accuracy of sampling a mine de- 
uends upon at least four factors, not one of which can be 
regarded as capable of being accurately computed. The 
estimation of the value of a body of ore in place to within 
one-fifth of one per cent, as appears to have been done by 
Mr. Hammond is certainly a remarkable result. 

To sum up the whole matter, it may be fairly stated that 
engineers’ reports upon the value of ore in sight can be 
considered nothing more than close approximations. If the 
work of a careful and conscientious engineer be examined, 
it will be found that whilst he may over-estimate in some 
cases, yet in others he will under-estimate, and if an aver¬ 
age bei taken his work will come out very close to the real 
facts. The more experience an engineer has, the more 
careful he becomes in making his examination, and the 
more he will lay stress upon the approximate nature of 
his figures. Many engineers are made the victim of sen¬ 
sational newspaper writers, who will take his figures and 
write into them ideas that the engineers would never 
indorse. Should an engineer come within a few dollars of 
the correct value of an ore in a mine, he, himself, would 
regard it a happy chance, and not as the result of any 
particular genius. He would regard an estimate which was 
ten per cent, too high, or ten per cent, too low, with equal 
complacency, because none would know better than he 
the approximate character of such estimations.—Ed. Min¬ 
ing Reporter.] 


ORE IN SIGHT. 


rs 


‘•AUDI ALTEREM PARTEM.”* 


Editor Mining Reporter: 

In your issue of January 2nd, 1902, a letter appears un¬ 
der the caption of “Mine Sampling Extraordinary.” In 
that letter there is much to which no engineer could take 
exception, but if you will allow me to say so, there is also 
much which flavors of hyper-criticism. Although not 
specifically stated, it appears that the letter refers to Strat¬ 
ton’s Independence mine at Cripple Creek. I feel sure that 
your sense of fairness will allow you to present another 
side of the case—for there is another side. The writer of 
the letter analyzes the outputs of the mine at various 
periods and compares them with the estimated tonnage 
and value. In a table it was shown that the examining 
engineer found 53,646 tons of ore with a value of $125 per 
ton. He assumed 70,000 tons at $95 per ton. The mine 
has actually put out, since the sampling, 129,615 tons, which 
gave a value of $53.38 per ton. Your correspondent asks: 
“What under heaven the sampling represented?” And he 
points out that the examining engineer reported that a 
given space would hold 53,000 tons of ore, and then as¬ 
sumes that it will hold 70,000 tons., 

To anyone familiar with the Cripple Creek District, 
these facts which appear so damning on the face are read¬ 
ily explained. In the first place it is ridiculous to suppose 
that any intelligent man would assume that a quart of 
whiskey can be placed into a pint bottle, and this feat is 
not under consideration. An examining engineer will value 
and measure a body of ore and find so many tons of such 
and such a value. The mine superintendent, who does the 
actual work of mining that ore, may decide that it is neces¬ 
sary to take out more of the low grade ore and waste in 
proportion to the high grade ore, in fact it may be abso¬ 
lutely essential to do so, thus running up the tonnage and 
lowering the value per ton. If we turn to the report we 
will find that on some of the levels the average width of 
the ore is only six inches, and in mining this ore' a great 
deal of waste or low grade material must necessarily have 
been taken out. If this is not so, then we have a feat 
which is more appalling than the pouring of a quart of 
whiskey into a pint bottle, or in other words we would have 
the acrobatic exploit of forcing a six-foot man into a six- 
inch space. At least two feet on each side of the six-inch 


♦Mining Reporter, January 9, 1902. 



14 


ORE'^IN SIGHT. 


streak of ore would be taken out. When this ore is sent 
to the sorting house, considerable screenings are made, 
which will be shipped, the ore only roughly sorted and thus 
the average value of the whole amount of ore shipped will 
be very much reduced per ton from that estimated. Your 
correspondent shows that 129,615 tons of ore were shipped 
of a value of $53.38 per ton, with a yield of $6,919,503. A 
mere rule of three sum will show that had the ore been 
sorted down closely to 53,646 tons that the ore would have 
been worth per ton $129, a difference of $4 per ton, or 
three and two-tenths per cent, from the estimate. 

The writer also refers to the matter of gross production, 
and this, in my judgment, should form the real basis -of 
criticism. The examining engineer found a gross value of 
$6,712,000. The mine has produced $6,919,603. There is 
yet in sight about $800,000, and we have it on the authority 
of Mr. Hammond that no additional ore has been put in 
sight during the last year. If we add $800,000 to the out¬ 
put to date, the mine will produce $7,700,000, but your 
correspondent says that considerable of this has been «^is- 
covered since the time when the ore was estimated; he 
also says that no one can examine a Cripple Creek mine 
and get a closer result than twenty-five per cent. In other 
words, if the mine had produced only $5,034,000, then the 
estimate made by the examining engineer could still be 
regarded as good work. This leaves a balance of $2,600,000 
between the lowest and actual result to have been dis¬ 
covered from March 18th, 1899, to November 1st, 1900. 
How much actually was discovered I do not know, and I 
think that but few other engineers know. But it seems 
to me that the sum of $2,600,000 would have more than 
covered the amount. 

To sum up the whole matter, it would appear from your 
corrospondent’s own letter that the engineer’s estimate of 
the value of ore in sight was not so far out as has been 
made to appear, and tnat the difference between tonnage 
of ore estimated in sight and that actually shipped is 
readily explained when we consider conditions of mining 
in Cripple Creek. g p 

[In accordance with the well-known policy of Mining 
Reporter we publish this letter, sent to us under the cap¬ 
tion given above, in answer to the letter of “Engineer,” 
published Januarj^ 2nd, 1902, as we believe that nothing 
but good can come from the discussion, and in all fairness 
and justice to both sides of this mooted subject.—Ed.] 


ORE IN SIGHT. 


15 


"‘MINE SAMPLING EXTRAORDINARY."* 

In your issues of January 2nd and 9th, 1902, there ap¬ 
peared letters relating to sampling of Stratton’s Independ¬ 
ence mine at Cripple Creek, the first letter being by “En¬ 
gineer,” and the second by “E. H. P.” The subject of “How 
to Sample a Mine” is of supreme importance, and it might 
also be said the subject of “How Not to Sample a Mine” is 
of equal- importance, and it sterns to me that engineers 
need cautioning on this matter more than on any other 
branch of their work. The letters referred to are evidently 
from men who are interested in this subject, and who ap¬ 
parently wish to thresh out in a spirit of fairness the 
merits of the methods adopted for the sampling of par¬ 
ticular mines. I have' a few words to say on the subject 
which I hope you will allow to be published. In the first 
place I would say that of all operations performed by en¬ 
gineers, none can be simpler than mine sampling. It 
simply requires the conscientious performance of a certain 
amount of hard work. In carrying out such work, haste is 
to be avoided, and the care with which the sampling of a 
large mine may have been conducted can be accurately 
gauged by the number of samples obtained in a given time. 
Another gauge which can be applied to the sampling of a 
mine is the accuracy with which duplicate assays made by 
different assayers agree. If these tests be applied to the 
sampling of Stratton’s Independence it will be found to be 
absolutely lacking in accuracy and to be indeed utterly 
worthless. 

Had the report of the examining engineer simply stated 
that the mine would produce $6,712,000 and had given no 
details of the method of sampling, it might appear as if a 
most excellent estimate had been made. But the horrible 
examples given in the report of the agreement between 
the various assayers show that the estimate was at best 
merely a lucky guess. Let me give a few of the examples. 

First as to the agreement between the assays. If we 
turn to the table of the assays we will find that scores 
disagree so much that it is surprising that any engineer 
could take the mean between the two. Thus: 


Sample, No. Assay 1. Assay 2. 

41.$280.00 $143.40 

304. 12.80 102.80 

337. 6.40 438.80 

386. 334.20 8.80 

424. 6.40 120.40 

518. 62.40 200.00 


♦Mining Reporter, February 6, 1902. 









16 


ORE IN SIGHT. 


And many others just as bad. It is absolutely absurd to 
say that where one assay gave $6.40 and another $438.80, 
both on the same pulp, that the average should be taken at 
about $224. Such a valuation as this vitiates the whole 
sampling, for either the value of the ore is approximate!}' 
$6 per ton, or approximately $440 per ton, and there can be 
no such value as $224. This latter value is entirely ficti¬ 
tious, and estimate® on ore in sight, based on such a value 
are utterly ridiculous. In such a case the assayers should 
be called upon to repeat their work, and if the difference 
were still shown by the repeat assays, the assay should be 
rejected and the mine resampled in those places where 
such variations were shown. This not having been done, 
and the fictitious values used, I therefore say that the 
sampling of the mine, including the very simple operation 
of dividing the pulp, was incorrectly and superficially per¬ 
formed. I 

The examining engineer in estimating the average value 
of the ore used' the old and well known metnod of foot 
ounces, that is to say, that in order to find the average 
value, of the ore mined, he multiplied the assays in ounces 
per ton by the width of the vein at the various places, and 
divided the sum of these products by the sum of the widths 
of the veins. 

Let us apply this method to the examples already given, 
using, however, the more usual method of dollar feet in¬ 
stead of ounce feet, we find the following results: 


Sample No. No. 1, Dollar Feet. No. 2, Dollar Feet. 

41.2,170 1,111 

304. 51 411 

337.:- 4 329 

386.2,005 52 

424. 17 770 

518. 78 250 


It is astonishing, to say the very least, to see an en¬ 
gineer take a mean between a sample which showed 4 
dollars feet, and one which showed 329, the ratio between 
the values being as 1 to 80. In 386 a mean was taken be¬ 
tween 2,005 and 52, a ration of 1 to 39 approximately. 
Such work as this is indefensible, and shows the crudity 
with which the work of sampling was performed. Further, 
if we work out the average value of the ore in assays No. l! 
we hnd an average of $192.20. In assays No. 2 the average 
value of the ore was $85.40. The mean of these two values, 
$138.70, is not very far from the average value of the ore 
as reported by the engineer, but surely anyone can see 








ORE IN SIGHT. 


17 


that it is not a question of avei’aging up of the value of 
the ore, but which of the two different estimates is correct. 
The whole business is perfectly farcical. That these re¬ 
marks are justified is to be seen from the results of min¬ 
ing. The question is not whether the mine has produced 
seven million dollars, or eight million dollars, but whether 
it produced 70,000 tons of ore at $95 per ton, as shown by 
the sampling, or the alleged sampling, performed by the 
examining engineer. To say that the mine produced a 
greater tonnage of less value, and hence the origir J 
sampling was correct, is simply ridiculous. In what leg ii- 
mate business would such work bei tolerated? If I buj a 
horse worth $200, I would not be satisfied with being j,ut 
off with two horses, each only worth $100, so if a mine is 
sold which contains 70,000 tons of ore worth $95 per ton, 
the purchaser is naturally not satisfied with a mine hav¬ 
ing three or four times that tonnage, of one-third or the 
one-fourth that value per ton. The question is not whether 
the mine produced a certain gross output, but whether the 
sampling of the mine was correctly done. 

Furthermore, E. H. P. did not touch on the point made 
by “Engineer,” that much of the ore mined and sent to the 
mills was eliminated from the examining engineer’s report 
as being below the limit of profitable mining. The engineer 
estimating the value of such ore at $20 per ton. From much 
of this ore of a value of less than $20 per ton, much of the 
gross output of the mine has been made. Therefore-, in 
order to see how close the original estimate was and the 
actual production, we have to deduct from the total output 
of the mine since the date of sampling, first, the value of 
the ores discovered since the date of sampling; secondly, 
the values obtained from the ores carrying less than $20 
per ton. Unfortunately, however, the published reports do 
not contain full enough information in order to allow this to 
be done, but if it could be, then the apparently wonderful 
agreement between the report of the examining engineer, 
and the actual production from the territory examined by 
him, would not appear to be so wonderful after all. 

E. H. P. states that Hammond’s report says that no ore 
discoveries have been made in Stratton’s Independence 
since he took hold of the mine. E. H. P. does not state the 
facts correctly. Hammond alluded to the southern terri¬ 
tory in which new work was being done. But in the report 
issued by the directors of the company for the year end¬ 
ing June 30th, but which has only just come to hand, hav¬ 
ing been issued on December 31st, we find that in the north- 


18 


ORE IN SIGHT. 


ern, or old, territory considerable discoveries have been 
made, and therefor much of the gross output of the mine 
has been made from discoveries made since the date of 
the first sampling. That there should be serious discrep¬ 
ancies between the estimated ore in the mine and the 
actual production is obvious to anyone who takes the 
pains to analyze the report I have been discussing. As 
this letter is already rather long I shall defer making fur¬ 
ther remarks, but shall have something more to say later. 

Denver, Jan. 31, 1902. ENGiNEER NO. 2. 


ORE IN SIGHT.* 


The term ‘^ore in sight,” as explained in a recent edi¬ 
torial, is not a happy one, yet it is so commonly used that 
we suppose that it will not be superseded at any rate for a 
long time. We suggest “estimated ore reserves” as ex¬ 
pressing more nearly what is meant. The ore should be ex¬ 
posed on three sides to be considered as a reserve and the 
blocks should not be too large. Where exposed on only two 
sides some judgment must be used and the reserve should 
be placed in a class by itself as “probable” ore reserve. 
Estimating the weight of the ore in the blocks is one of the 
calculations most subject to error, being only second to 
the errors of sampling. After the cubic contents of the 
block has been determined it is necessary to find the num¬ 
ber of cubic feet to the ton. It is too common for engineers 
to guess at this; thus, fourteen cubic feet for quartz and 
eight cubic feet for heavy sulphides, and so forth. From 
the writer’s own experience the following figures are given 
to show how very varied results are obtained. Quartz, 13.2 
cubic feet, 16.5, 14, 13.5, 17; decomposed surface ores, 14 to 
21 cubic feet; sulphide ores, such as iron and copper 
pyrites, 7.2, 12, 11.2, 11.7, etc. The writer’s practice is to 
take a number of characteristic specimens from the sam¬ 
ples of each block of ground and determine the specific 
gravities, using the mean from the samples for the block 
from which they were taken. To show the effect of varia¬ 
tion. A block of ground contains 30,000 cubic feet of ma¬ 
terial; the ore contains thirty-five ounces silver per ton. 
We assume 13 cubic feet to the ton; therefore the block 
contains 2,300 tons, in which there are 80,500 ounces of sil¬ 
ver, and we so report. Now suppose the ore measured 
actually 20 cubic feet to the ton; then there would be only 

*Mining Reporter, May 22, 1902. 





ORE IN SIGHT. 


19 


1,500 tons of ore and 54,500 ounces of silver. Such a differ¬ 
ence as this is enormous and may make such a radical dif¬ 
ference as to cause much loss of money to the purchaser 
and the loss of reputation to the engineer who made the 
report. 


ORE IN SIGHT.* 


In our issue of March 20, 1902, we published a paper 
read by J. D. Kendall before the Institution of Mining and 
Metallurgy, in which he called attention to the use of the 
term “Ore in Sight.” The importance of Mr. Kendall’s 
remarks cannot be overestimated and we append the latest 
ruling of the society in regard to the use of this term, in 
which it strictly defines the limits wherein the use of the 
term is justifiable, and unmistakably puts itself on record 
as opposed to its indiscriminate use, defining such as a 
sign of dishonesty or incompetency where it is used with 
the slightest ambiguity or mystery. 

“Ore in Sight.” 

The council of the Institution of Mining and Metallurgy 
recognizing the great importance, to the mining industry 
and to the public generally, of the subject dealt with in 
the paper on “Ore in Sight,” by Mr. J. D. Kendall (“Trans¬ 
actions,” Volume X). appointed a committee to consider 
what steps the institution might usefully'take in defining 
the term “Ore in Sight.” 

The views expressed by leading members of the pro¬ 
fession showed a great divergence of opinion as to the defi¬ 
nition of the term. 

After due consideration and discussion the council came 
to the following decision: 

1. —That members of the institution should not make 
use of the term “Ore in Sight,” in their reports, without 
indicating in the most explicit manner, the data upon 
which the estimate is based; and that it is most desirable 
that estimates should be illustrated by drawings. 

2. —That as the term “Ore in Sight” is frequently used 
to indicate two separate factors in an estimate, namely: 

(a) Ore blocked out—that is ore exposed on at least 
three sides within reasonable distance of each other; and 

(b) Or which may be reasonably assumed to exist 
though not actually “blocked out,” 

these two factors should in all cases be kept distinct, as 


♦Mining Reporter, October 30, 1902. 





20 


ORE "IN SIGHT. 


(a) is governed by fixed rules, whilst (b) is dependent upon 
individual judgment and local experience. 

3. —That in making use of the term “Ore in Sight,” an 
engineer should demonstrate that the ore so denominated 
is capable of being profitably extracted under working con¬ 
ditions obtaining in the district. 

4. —That the members of the institution be urged to 
protect the best interests of the profession by using their 
infiuence in every way possible to prevent and discourage 
the use of the term “Ore in Sight” except as "defined above; 
and the council also strongly advise that no ambiguity or 
mystery in this connection should be tolerated, as they 
(the council) consider that such ambiguity is an indication 
of dishonesty or incompetency. 


ORE IN SIGHT.* 


In our issue of October 30th we reprinted the report 
issued by the committee, appointed by the Institution of 
Mining and Metallurgy, to define the term “Ore in Sight.” 
During the early part of the year we went very fully into 
this question. We expressed an opinion, at that time, that 
the term “Ore in Sight” was an unfortunate choice of 
words and that a new term, such as “Estimated Ore Re¬ 
serves,” should be adopted. We do not think that the re¬ 
port issued by the committee of the I. M. and M. has done 
much to clear up the atmosphere, although it has, of 
course, some value. Take for example section 2, paragraph 
(a), which reads; 

“(a.) Ore blocked out—that is ore exposed on at least 
three sides within reasonable distance of each other.” 

One would assume from this paragraph that any block 
of ground opened up on three sides could be considered 
“in sight,” and that the cubic contents of the block multi¬ 
plied by the average value of the edges would give the 
total value of the, ore “in sight.” This is a fallacy upon 
which many a promising enterprise has been wrecked. It 
is the more dangerous because it is so plausible. 

Let us look for a moment at the language of the report. 
The ore is considered in sight when at least three sides of 
a block are “within reasonable distance of each other.” 
Why this restriction as to distances between the sides? 
So far as we can see the committee wished to call atten¬ 
tion to the error of estimating too large an amount of ore 


*Mining Reporter, November 13, 1902. 





ORE IN SIGHT. 


21 


in one block as thereby there is evidently more chance of 
the block being composed of heteregeneous matter and 
thus the errors of estimating may be abnormally large. 

Now, what can be considered a “reasonable distance” 
between sides? We know of cases where blocks of con¬ 
siderable size may be considered as estimable and others 
where we would feel very doubtful as to the reasonability 
of the ore. being sufficiently developed to allow of close 
calculations being made, even if the sides were compara¬ 
tively close together. The closer the sides are together the 
smaller the block and the greater becomes the homogeneity 
of the mass of ore to be estimated. The homogeneity of 
the block, hence, appears to be the crux of the matter and 
not the size. 

Suppose the ore blocked out showed that, for example, 
the lower edge exposed ore of very different value and 
character to that exposed by the upper edge. Can w€ 
figure in this case on the block being “in sight,” especially 
if one or the other of the edges exposed ore. of less than pay 
value? We think not, and an article, for which we have 
no space this week, goes into detail and explains why 
not. It is laid down in this article referred to, that the 
size of the block should not be the criterion of the ore 
being within reasonable calculation, or not, but that rather 
the uniformity of the ore composing the block should be 
considered. This definition allows, too, of the engineer 
being able to apply a direct test as to whether the block 
may be reasonably “in sight” or not. The definition should 
be rather 

“Ore blocked out”—that is ore sufficiently developed 
to enable the engineer to sample upon three sides of a 
block, so as to determine the distribution of values and 
the uniformly pay character of the ore, or otherwise. 
Should the assay chart show that much of the ore is below 
pay value, then sufficient development work should have 
been done so as to determine, with reasonable accuracy, 
the lines of contact between the pay and non-pay ore. 

Those interested in this very interesting subject may 
refer to the editorial which appeared in Mining Reporter 
January 2, 1903. 


CHAPTER I. 


DiiriEg the last eighteen months one of the most interest¬ 
ing topics of discussion amongst mining engineers has been 
the methods of mine examination and the degree of accuracy 
with which the tonnage and ore values can be determined 
in a developed mining property. In these discussions Min¬ 
ing Reporter has borne a leading part. As is inevitable in 
such cases the writers, most of them prominent in the 
mining world, have presented many interesting facts, the 
value of which have been lost, to a very large extent, by the 
lack of connection between the various contributions to this 
journal. In a recent issue there was reprinted on the edito¬ 
rial page the report of a committee appointed by the Council 
of the Institute of Mining and Metallurgy of London, Eng¬ 
land, to consider the question of formulating a ruling, to 
which the members of that institution should conform, on 
what constitutes “Ore in Sight.” The report, coming from 
such an authority, naturally carries a great deal of weight, 
not only with professional men, but with the investing pub¬ 
lic. Should, therefore, the rulings be ill-advised the pro¬ 
fession at large will be burdened with the incubus of incor¬ 
rect methods and both the investor and engineer will suffer. 

Under these circumstances the writer has thought it time¬ 
ly to connect the discussions which have been going on in 
Mining Reporter for such a length of time, and to discuss, 
somewhat fully, the rulings of the committee of the Institute 
of Mining and Metallurgy. Before doing so, however, it should 
be stated that the profession at large owes a great debt to 
the institute referred to by taking up the consideration of 
a question so vital to the mining industry as the valuation 
of ore exposed in underground workings. To the writer the 
report is not as satisfactory as it might be, and he trusts 
that the committee may see its way to amend the rulings 
so as to cover the ground more adequately. 

The valuation of a mine is, by a general concensus of 
opinion, one of the most difficult tasks that can be set to a 
mining engineer. Every reputable engineer feels that when¬ 
ever he undertakes a mine examination he is liable to jeop¬ 
ardize a reputation built up by years of good and faithful 
work. He knows, too, that he may be victimized by misrep¬ 
resentation, and be made a scapegoat for incompetent man¬ 
agement with which he may have had nothing to do. The 



ORE IN SIGHT. 


2:^ 


writer knows of a case in which a thoroughly competent 
Australian engineer was made to sulfer, by the “operations*” 
of a stock trading gang, for doing unusually sound mining 
work. A Denver engineer, some years ago, had his report, 
which was almost absolutely borne out by the after opera¬ 
tions of the mine, so misrepresented that he suffered to a 
very considerable extent. His business associates, however, 
knew the facts and the effect of the misrepresentations 
gradually wore off. 

In addition to the dangers just touched upon, the en¬ 
gineer knows that he is liable to run up against a very 
difficult problem, which he has to solve with, often, very- 
inadequate means. The problem is solved as well as the 
circumstances will admit, but future development may show 
that on some matters he was not strictly correct. In most 
cases the people for whom he did the work would appre¬ 
ciate the circumstances and nothing w'ould be said or felt 
to the detriment of the engineer’s reputation. But suppose 
that for some reason, say poor management or “exigencies” 
of the stock market, a scapegoat has to be found, who 
suffers? The examining engineer, of cour<^e. 

Then, too, a failure is read of in the newspapers with 
so much more relish than a success, and therefore such news 
is scattered far and wide with a slight misrepresentation 
added at each repetition. On the other hand, a paragraph 
in a paper laudatory of the engineer’s work is often taken 
to be judicious log rolling and little, if any, notice is taken 
of it. Thus a man after twenty years of successful work 
may find himself known as the engineer who was tripped 
up in such and such an examination a short time ago. 

The work of examining a mine is, as stated above, very 
difficult and tedious. This is rendered so by the complexity 
of the problems set in working out the value of the ore 
which has been so thoroughly exposed by mining operations 
that a miner would feel justified in saying that such and 
such an amount of ore can be taken out. In other words, 
by the difficulty of estimating the amount and value of the 
“ore in sight.” The task is not rendered any easier by the 
fact that there is no uniformity of ideas upon what act¬ 
ually constitutes such ore. The term is used very compre¬ 
hensively by some engineers, notably the English, and in a 
very circumscribed manner by others. By careless engi¬ 
neers it is used so recklessly that the term fails to have 
any significance but “the amount of ore guessed at.” This 
latter is criminal incompetence, or worse. 

The term, “ore in sight,” is one which has unfortunately 


24 


ORE IN SIGHT, 


been so much misapplied that it has come to be an object 
of derision amongst investors and those who dabble in min¬ 
ing. I have now before me a number of letters in which 
this term is treated with scant courtesy. Two extracts from 
different letters show the general trend of the remarks. In 
one a well-known promoter says: “I regard ore in sight as 
a^very uncertain quantity.” In another a first-class lawyer, 
with a wide experience in mining operations, said: “I re¬ 
gard ore in sight as furnishing merely a pointer, and not as 
an exact term. I have seen it used so many times and so 
rarely have the figures been correct that I believe it is but 
little more than a guess.” ^ 

The phrase, “ore in sight,” is, in my judgment, a very 
unfortunate one; it has been so much abused and has been 
so loosely applied that it would be better to drop it alto¬ 
gether and use some new term which not only correctly 
defines what the engineer means, but which has not the 
odium attached to it that the present one has. As a matter 
of fact the ore reported upon by an examining engineer is 
not in sight nor can it be until it is mined, crushed and sam¬ 
pled, and assayed. The mere fact of calling it “in sight” 
does not render it any the more within the limits of vision. 
A recent writer has suggested that the phrase means “in 
the mind’s eye.” If this is so,, why not report it as such? 
Then^.,the engineer’s clients would be charmed to know that 
he finds “in his mind’s eye” so many tons of ore worth so 
many dollars. . 

The public is very apt to take technical language literally 
and _(When an engineer reports so many tons of ore “in 
sight” the technical restriction to ore in the mind’s eye is 
not likely to be understood. The term had better go, and 
the writer, who has until recently conformed to the general 
custom, has decided to relinquish the use of it. A quotation 
from Mining Reporter of January 2nd last will supply some 
terms which are much more expressive of what an engineer 
really means than the condemned term. 

“We are strongly of the opinion that the term ‘Ore in 
Sight’ should be abandoned, and replaced by some term 
which more nearly represents the fact. We suggest that 
some such prases as ‘Estimated Ore Reserves,’ ‘Probably 
Pay Ore,’ ‘Estimated Tonnage of Ore,’ would more closely 
represent what the engineer really means to say than the 
term ‘in sight.’ For the protection of the public, who are 
not likely to know the technical restriction of the words 
‘in sight,’ some such phrases as we have suggested should 
by all means be adopted.” ^ 


ORE IN SIGHT. 


2o 


Before considering the measurement of ore and the deter¬ 
mination of its value it might be desirable to see what is 
understood by the term “ore in sight.” As usually defined, 
it means that three sides of an ore body are exposed by de¬ 
velopment work; that these sides are measured, sampled 
and assayed at regular intervals. The cubic contents of the 
block, as determined by the measureiments, divided by an 
arbitrarily imagined weight per cubic foot gives the tonnage 
of oie “in sight.” Multiply this tonnage by the value of 
the ore and a figure is obtained called “the value of the ore 
in sight.” 

E. B. Kirby, in a well-considered paper read before the 
Coloiado Scientific Society, defined “ore in sight” as “that 
contained in blocked portions of the deposit, each of which 
is so clearly exposed that the limits, continuity and value 
of its contents may be determined upon with reasonable 
certainty.” This definition is an excellent one, and with 
some restrictions upon its application may well be adopted 
by the profession at large. As we shall see later, the correct 
application of this definition will give very different results 
to those obtained by. following the definition given above. 

We now come to the report of the committee of the In¬ 
stitute of Mining and Metallurgy. The ruling of this com¬ 
mittee is as follows: 

“2.—That as the term ‘Ore in Sight’ is frequently used to 
indicate two separate factors in an estimate, namely: 

“(a) Ore blocked out—that is ore exposed on at least 
three sides within reasonable distance of each other; and 

“(b) Ore which may be reasonably assumed to exist, 
though not actually ‘blocked out.’ 

“These two factors should in all cases be kept distinct, 
as (a) is governed by fixed rules, whilst (b) is dependent 
upon individual judgment and local experience. 

“3.—That in making use of the teim ‘Ore in Sight’ an 
engineer should dem-onstrate that the ore so dominated is 
capable of being profitably extracted under working condi¬ 
tions obtaining in the district.” 

The language of this report is ambiguous. Does ruling 
2 mean that “ore in sight” includes: 

(a) Ore blocked out. 

(b) Ore which may be reasonably assumed to exist, and 
that the practice of lumping these two factors together is 
to be condemned and that the correct method is to report 
“ore in sight” under the headings of (a) and (b)? If 
so, this ruling is a very unwise one, since it is very apt to 


ORE IN SIGHT. 


2G 


mislead the investing public. Or does the ruling mean that 
the practice of reporting “ore blocked out” and “ore as¬ 
sumed to exist” as being “in sight” is disapproved of? If 
so, the ruling should be amended to: 

“The term ‘ore in sight’ being frequently used to include 
ore ‘blocked out’ and ore ‘assumed to exist.’ this practice is 
disapproved of and the term ‘ore in sight’ should be re¬ 
stricted to the ore which is blocked out. The ore which 
may be reasonably assumed to exist, though not actually 
blocked out, should in all cases be reported upon under the 
head of speculative values or an equivalent term.” 

The first reading given to the committee’s report by the 
writer favored the first interpretation, and most people 
would take it to mean this. In all probability, therefore, 
the committee means the members of its institute to report 
as follows: 

“Ore in Sight”— 


(a) Ore blocked out. . tons 

(b) Ore assumed to exist. . tons 

Total . . tons 


Now we have the definitions of “ore in sight,” and let us 
assume that we have three engineers reporting upon the 
same mine and that each was capable and honest. The re¬ 
ports would be, in all probability, so different that the in¬ 
vestor would not know what to make of the situation. For 
engineer No. 1, using the first definition, would report so 
many thousands of tons, whilst engineer No. 2 would throw 
out a great deal of the ore reported upon by No. 1, and then 
engineer No. 3 would show all the ore reported upon by 
No. 1, with some more added. 

Such a condition of affairs is unsatisfactory, to say the 
least, and it is highly important that the ambiguity should 
be removed. It is certainly not to the interests of the 
profession that the public should have no confidence in re¬ 
ports of ore values, or that the investor should be required 
to unravel the tangle for himself. 









CHAPTER II. 


In the preceding chapter much has been said regarding 
the leeling of insecurity with which ore measurements 
and values are regarded by investors and by quite a few 
mining men themselves. Before dealing with the meas¬ 
urements, etc., it might be advisable to give some examples 
as to the accuracy attained in a large number of cases. 
The cases in which the competent engineer makes a re¬ 
markably correct estimate are very much more common 
than one would suppose from current literature. Very 
little is said when engineers are correct in their estimates. 

The first examples to be given are taken from South 
African practice. Owing to the presence in South Africa 
of so many eminent and thoroughly practical engineers 
some most excellent work has been done in those fields. 
The records of these men are fortunately made available 
for their foreign confreres by the publications of the South 
African Technical Societies, the energetic mining associa¬ 
tion at Johannesburg, and lastly, but not least, by the re¬ 
ports of the various companies operating in the vicinity of 
Johannesburg and elsewhere. 

During the period whilst the so-called “Deep Levels” 
were being opened up in and around Johannesburg, es¬ 
timates were made as to the values of the respective areas 
being developed. Since that time many of these deep 
levels have commenced operations and it may be interest¬ 
ing to compare the estimated recoverable values and the 
actual values recovered. The following table, originally 
compiled by S. J. Truscott, shows the estimated values 
and the actually recovered values during the first five 
months of 1898. To this table I have added the percentage 
errors: 


Mine— 

Crown Deep. 

RoDinson Deep .. 
Nourse Deep .... 
Jumpers Deep .. 
Goldenhen’s Deep 
Rose Deep. 




a 

r-t- 

< 

to 

o 

p 


p 


3 



p 



(—*■ 



a> 


w 

& 


B. 







O 


P 

O 


cr; 

O 


to 

< 



tt) 






P 


a] 


(D 



>-i (T> 


48 

60 

48 

35 

36 
40 


> 
w O 

M P 


39.38 

63.10 

47.45 

43.42 

38.81 

44.30 


5^ 

o 


—17.9 
+ 5.1 
— 1.1 
-f24.0 
-f 7.9 
-flO.7 


Average 


44.5 46.07 -f 3.3 














ORE IN SIGHT. 


2S 

Ihe average derived from the six great mines showed 
that, taken as a whole, the stockholders were receiving in 
1S93, 3.3/0 higher values than were promised by their 
engineers. This is remarkable work when we consider 
that these values do not represent gross values, but net 
returns. If it is difficult to determine gross values (as it 
is) it must be more difficult to take these primary figures, 
make the necessary tests and calculations and finally to 
determine the commercial yield of a body of ore yet un¬ 
mined. The probabilities of error are greatly multiplied. 
Under these circumstances the degree of accuracy attained 
by the South African engineers is very creditable and 
shows what can be done when careful work is performed. 

It might be claimed that the South African ores are 
very uniform in character and hence the errors are not 
subject to those disturbing influences which are the bane 
of the engineer in fissure veins. There is an element of 
truth in such objections and the writer therefore will give 
three other examples shov/ing the degree of accuracy which 
can be attained in mine examination. Selecting three en¬ 
tirely different types of deposits in widely separated dis¬ 
tricts. In 1893 Mr. E. S. Peters made an examination of 
the Mount Lyell copper mines in Tasmania. The actual re¬ 
sults as produced on a working scale were wonderfully 
close to those estimated by the engineer. The ore is 
smelted at the mine and converted by Bessemerizing into 
crude copper. The estimates included the cost of working 
and about three years after it was found that Mr. Peters’ 
estimates were verified within 161^ cents per ton. The 
original estimates and those for six months’ consecutive 


working are given below in 

parallel columns: 



Estimated, 

Actual, 


1893. 

1897. 

Mining. 

. 30.0d 

3s 8.27d 

Smelting. 

. 16.6d 

18s 1.64d 

Bessemerizing. 

. 5.6d 

3s 10.39d 

Totals. 

. 25.0d 

25s 8.30d 

The estimates as to the 

ore values were even more re- 

markable: 

Estimated, 

Actual, 


1893. 

1897. 

Copper . 

. .. 4.5 % 

4.5 % 

Silver. 

. . . 3.0 ozs. 

3.75 ozs. 

Gold. 

. . . 2.5 dwts. 

2.0 dwts. 


These results compare well with the estimates made in 
any other business, whether railroading, electric lighting. 











ORE IN SIGHT. 


29 


farming or general merchandising. No conservative busi¬ 
ness man goes into any enterprise without preliminary 
figuiing, and the opinion can be freely hazarded that if 
the business man’s estimates came out, at the end, as cor¬ 
rectly as Mr. Peters’ in the example just cited, the busi¬ 
ness man would feel that he had done wonderfully well. 

The other example is of a Colorado mine. In 1?92 Mr. 
Philip Argali examined the Tom Boy mine, then only par¬ 
tially opened up, but sufficiently so to allow a careful en¬ 
gineer to estimate, with reasonable accuracy, the amount 
of ore exposed and its value. The report made by Mr. 
Argali was verified very closely both in respect to tonnage 
as well as to value. Indeed the value reported by Mr. 
Argali was $9.50 per ton, and the actual values of the ore 
as mined were $9.39 per ton, as shown by the reports of the 
company’s work. 

The other example is the Minah mine in Montana. A 
certain amount of ground was opened up, which, according 
to measurements and assays, contained 9,700 tons worth 
$18.45 per ton, or a gross value of $178,965. The actual 
amount taken out of this ground was $235,000, of which 
$45,000 was from new discoveries and ore which at the 
time of examination was too low grade to pay. The amount 
taken out of the measured ground was therefore $190,000, 
or 6%% more than was estimated. 

’ihese examples are but a few of the many that could 
be given, and if engineers could be persuaded to publish 
the results as obtained by their examinations and those 
obtained by actual mining work the writer does not doubt 
that it would be seen that competent men do not make as 
many errors in this very important work of determining 
tonnage and values as one might think. Unfortunately we 
generally only hear of errors when they are against the 
investor and rarely, or never, hear of the correct results. 

It should be pointed out that one of the greatest draw¬ 
backs to mine examination is frequently the very inade¬ 
quate time allowed. No work that an engineer can engage 
in requires more care than mine examination. He is fre¬ 
quently called upon to examine a mine in a few days that 
an owner has been “fixing up” for sale for several years. 
The utmost vigilance is required in order to penetrate the 
disguise, if one may call it so, that is often thrown over the 
property. Of course the disguise is in favor of the mine. 

Then he must properly guard his samples. Salting, as the 
writer freely testifies, is very much less common than is 
supposed, but still it is a possibility always to be guarded 


80 


ORE IN SIGHT. 


against. The physical strain of taking samples, making 
measurements and penetrating the innermost recesses of 
the mine is very great. Yet withal the engineer must keep 
his head clear to unravel very often a most complicated 
vein structure. The expense of such work is considerable, 
both for assistance and assaying, as well as for the other 
items which are inevitable. If mistakes in mining are to 
be avoided the logical way to do so is to have a thorough 
preliminary examination. If a fair fee is paid for such 
work and a properly drawn up contract passes between 
the engineer and the party for whom the examination is 
being made, good results can be expected. Frequently 
engineers are expected to make an examination for a fee 
which would hardly cover their assay bill if the work is 
done correctly. 


CHAPTER III. 


Having now considered the subject of ore valuation in 
general, we may proceed to discuss the details of the work 
involved in maasuring and valuing ore bodies. 

The price at which a mine may be purchased depends 
upon many factors, the chief of which are: 

1— The amount and value of the ore so thoroughly de¬ 
veloped that an experienced miner is justified in believing 
that a certain tonnage of a given value, as determined by 
measurement, sampling and assaying, can be obtained out 
of the blocks opened up. In other words, what an American 
engineer calls “ore in sight” and the English engineer ore 
“blocked out.” 

2— The possibility of opening up of new ore bodies. This 
is, in turn, dependent upon many conditions which will be 
later considered in more detail. 

3— Upon local conditions arid the character and nature 
of the ore. 

l 

4— The price the owner thinks he ought to get for the 
property. 

Of these considerations the first will be here discussed in 
detail and it might here be stated that two reliable engi¬ 
neers should agree very closely in their estimates on such 
ground. 

Ore blocked out is defined by the committee of the Insti¬ 
tute of Mining and Metallurgy as being that which “is ex¬ 
posed, on at least three sides, within reasonable distance 
of each other.” It may be added that this is also the gen¬ 
erally accepted definition and that it is not here disputed. 
Four sides are, of course, really necessary to have ore com¬ 
pletely blocked out, but generally an engineer can arrive at 
definite conclusions when three sides are exposed for meas¬ 
urement and sampling. 

It is, however, usually concluded that the average value 
of a block of ground is the mean of the values of all the 
samples taken around the perimeter. This, in the writer’s 
judgment, is a fallacy which is responsible for many errors 
in determining the value of ore blocked out. 



ORE TN SIGHT. 


H2 


Absolute accuracy of estimates of ore values is not guar¬ 
anteed by examining engineers, nor is it expected by the 
parties for whom the examination is made. It is granted 
that the behavior of ore bodies is so eccentric that no engi¬ 
neer can look through the ground and tell exactly how the 
deposit is going to change. Because, however, nature 
chooses to throw obstacles in the way of. engineers that is no 
excuse for them to use inaccurate methods. It'is unscientific 
to argue that if certain natural difficulties exist it is useless 
to use exact methods of work, because the result of our 
calculations cannot be correct in such a case. Should we 
not rather argue that if nature is so unkind we ought to be 
much more careful in our methods so as to get as near the 
truth as possible? Two errors make a correct result, if they 
balance, but if the two errors are on the same side then we 
aie apt to make a disastrous mJstake. Now if it can be 
demonstrated that by using the three sides of a block of 
ground as the basis of our calculations we get as many 
different results as the possible number of permutations and 
combinations, then it must be evident that the method is 
fundamentally inaccurate. 

I et us take a block of ground A, B, C and D, as in Pig. 
1, of which A. B and D C are 300 feet in length and B C, 
A D are 100 feet in depth. We will give; 



This block of ground (from a case in the author’s ex¬ 
perience) contains the following values: A B $32; B C $10; 
C D $21, and A D $22 average per ton. The ore measured 
12 Cu ft. to the ton. We will proceed to calculate the value of 
the “ore in sight,” or shall we say “second sight,” when dif¬ 
ferent sides are opened up. The ore averages two feet in 
width. 








ORE IN SIGHT. 


33 


We will first take it that A B, B C and D C are the sides 
opened up, as in Fig. 2. 


Lsz r~~ . . B - 


To ~C 

Figure 2. 

Now we have the following tonnage in the block: 

300x100x2 60000 

---- 5000 tons. 

12 12 

The average value of the whole block can be obtained by 
the following method: 

0 D—21x300= 6,300 
B 0—10x100= 1,000 
^ r -32x300= 9,600 


700 16,900 

And dividing 16,900 by 700 we get $24.14 per ton as the 
average value. The value of the block (5,000 tons) is there¬ 
fore $120,700 gross—result No. 1. 

Let us have, now, the sides A B, A D and D C opened up. 

(See Fig. 3.) 















Figure 3. 


And then calculate the value. The tonnage is assumed to 
be 5,000 tons, as before. The average value of the block is 
calculated as before: 

A B—32x300= 9,600 
A D—22x100= 2,200 
D C—21x300= 6,300 


700 18,100 

Average value of $25.85 per ton. 

The total value of the block is now $129,250—result No, 2 
Let us now take the case when A D, D C and C B are the 
sides opened, (Fig. 4.) 



Figure 4. 
























ORE IN SIGHT. 




Then we have an average value of: 

A 0—22x100=2,200 
D 0—21x300=6,300 
B 0—10x100=1,000 


500 9,500 

Average value $19.00 per ton. 

The total value of the block in this case is $95,000—re¬ 
sult No. 3. 

We will take the last combination as the sides A B, A D 
and B 0 being exposed. (Pig. 5.) 



Figure 5. 


Then we have an average value of: 
A B—32x300= 9,600 
A D—22x100= 2,200 
B C—10x100= 1,000 


500 12,800 

Average $25.60 per ton. 

The block contains a gross value of $128,000—result 
No. 4. 

To recapitulate, we have the same block of ground yield¬ 
ing, by the rule generally approved of, the following diverse 
results: 


Gross Value 

Value. Per Ton. 

2 . 129,250 25.85 

1. $120,700 $24.14 

3 . 95,000 19.00 

4 . 128,000 25.60 


These are absurd differences, and if engineers cannot 

















ORE IN SIGHT. 


m 

devise some better rule than the one we have been consid¬ 
ering it would be better to discard the pretense of ore 
measurement and sampling and speaking of the value of 
“ore in sight.” To have the power to see $129,250 in one 
case and only $95,000 in another in the same block of ground 
savors of humbug. In order to make a clear exposition a 
very simple case has been taken, viz.: when the ore is of 
uniform width all around the perimeter of the block. Again 
taking a case from actual experience, wew ill assign different 
widths to the edges of the block, thus: A B 1.7 feet; A D 
2.2 feet: D C 2.2 feet; B C 3.5 feet. Let us calculate the 
value of the block under the different conditions as already 
considered, giving the calculation in detail for the first case 
only. (See Fig. 2.) 

In order to get the average width of the ore the average 
width of each edge is multiplied by the length of each edge 
and the totals of such amounts is divided by the total 
lengths, thus: 

A B—300x1.7= 510 

BC—100x3.5= 350 

CD—300x2.2= 620 

700 1,480 

Average width, 2.11 feet. 

The tonnage of the block is now: 

300x100x2.11 

- = 5,275 

12 

To obtain the average value of the ore in this case we 
have to use a figure, obtained for each edge, found by multi¬ 
plying the length by the average width, as above. This 
figure is used just as the length was in the previous exam¬ 
ples. We then find the average value of the ore in the case 
we are considering as follows: 

A B—32x510=16,320 

B C—10x350= 3,500 

C D—21x620=13,020 

1480 32,840 

Average value, $22.12. 

With a contents of 5,275 tons we have a gross value of 
$116,683—result 1. 

Calculating the other cases already cited whe have the 
following results: 






ORE IN SIGHT. 


37 


Tons. 


1 .5,275 

2 .4,800 

3 .5,950 

4 .5,400 


Val. Per Ton. 
22.12 
25.31 
18.78 
22.83 


Gross Value. 
$116,683 
121,488 
111,741 
123,282 


These figures are but the starting point, however, in cal¬ 
culating the value of a block of ground. The prospective 
purchaser is not particularly desirous of knowing the gross 
value of an ore deposit, but rather what he may expect to 
get out of it for himself; in other words, the net value. 
Now if we estimate the total cost of treatment per ton at 
$10.00 the net values of the block, according to the different 
conditions, are: 


Condition 1. $63,933 

Condition 2. 73,488 

Condition 3. 52,241 

Condition 4’. 69,282 


A maximum of $73,488 and a minimum of $52,241 is too 
great a difference and any rule which may give such a 
variation is the same block of ground is, in the writer’s 
judgment, a very dangerous one. 










CHAPTER IV. 


That the method of calculating the value of the ore 
reserves of a mine by averaging the assays of the peri¬ 
meters of a block is incorrect, has been demonstrated in 
the preceding chapter. It now remains to give an example 
of a mine examination by this method and to compare the 
results of working with the estimate made six years before 
the block reported upon was worked out. 

The drawing (Fig. 6) shows the condition of the mine 
in 1E91, and the numbers along the levels and down the 
winze give the points sampled. The block was an enormous 
one, being over 600 feet in length and 300 feet 
in depth, the contents being calculated at 30,000 tons. 
The value of the ore was put at $24.50 per ton, and the 
value of the block at $735,000. The engineer was justly 
criticised for attempting to estimate such an enormous 
block, but even so, if he had used a correct method of 
calculating the value he would not have ma^e anything like 
so grave an error as was demonstrated by later work. 

In. 1897 the block of ground was worked out and it then 
presented the appearance as shown by the longitudinal sec¬ 
tion in Fig. 7. The amount actually yielded by the block 
was about $180,000, much of which came from new discov¬ 
eries, chief of which was a bonanza bunch found outside 
the hanging wall by fortunate crosscutting. 

If Fig. 7 be examined it will be noticed that between the 
two cross-courses no ore was taken out other than that 
removed whilst driving exploring drifts. In not one of 
these drifts was pay ore discovered, and since every ton 
removed from the block near these drifts would have 
caused a loss of $2 a ton, the ground was left standing. 
Between the main winze and cross-course 1 (see Fig. 6) 
an approximately rectangular mass of ground was left 
standing as being of too low grade to remove. Hence in¬ 
stead of mining 30,000 tons, only some 10,000 tons was 
taken out of the ground. 

In discussing this piece of ground with different en¬ 
gineers the objection has been raised that the error was 
made through the examiner taking such a large block of 
ground as being available for measurement and calculation. 
This may be conceded so far as the enormity of the error 
is concerned (as measured in dollars and cents), but if the 



N 


ORE IN SIGHT, 


39 




























40 


ORE IN SIGHT. 


block of ground were only 300 feet in length and 100 feet 
in depth, and the same methods of calculation were 
adopted, even then the engineer would have found four 
times as much ore in the block as would or could be taken 
out at a profit. 

This being an admirable example of the fallacy of aver¬ 
aging the assays of the perimeter of a block, we will as¬ 
sume that in It91 the piece of ground measured 300 feet 
in length and 100 feet in depth, but was otherwise exactly 
as is shown in Fig. 6. Instead of having 180,000 square 
feet of stoping ground, as formerly, the reduced scale would 
show only 30,000 square feet, or one-sixth as much ore. 
There would be 5,000 tons. At $24.50 per ton this would 
represent a gross value of $122,500. Then reducing Fig. 7 
to the same scale we find that only 1 660 tons of ore would 
be moved from the block with a value of $30,000. Of course 
instead of an error of halt a million dollars the engineer 
would have miscalculated to the extent of only $92,000. 
The percentage of error would, however, still be the same. 
As we are not considering the magnitude of financial losses 
.but rather the accuracy with which such work is done, we 
must condemn the method of averaging the perimeter in 
order to ascertain the value of a block of ground. There 
is one exception to this rule, however, when the average 
of the perimeter will give fairly correct results, but this is 
of such rare occurrence, in this country at all events, that 
it will be considered, as an exception, later on. 

It may be asked if the method of averaging the 
perimeter be incorrect, how should one estimate the value 
of such a block of ground? In answer to this it should be 
first stated that the block is insufficiently developed to 
allow of close calculation. It is, however, presumable that 
some idea is required of the possibilities and hence some 
estimate must be made by the examining engineer. We 
will, therefore, make an attempt to put some kind of value 
on the ground and to forecast the amount of ore which 
may be mined from it. 

Taking the assays from samples 1 to 55 and plotting 
them on the longitudinal section we first endeavor to find 
the distribution of values. The writer’s note books show 
the following values: 


Assays 1 to 11 inclusive.$ 9.15 per ton 

Assays 11 to 24 inclusive. 38.50 per ton 

Assays 25 to 27 inclusive. 34.25 per ton 

Assays 27 to 30 inclusive. 8.30 per ton 

Assays 31 to 47 inclusive. 28.50 per ton 

Assays 48 to 55 inclusive. 8.75 per ton 








ORE IN SIGHT. 


41 


The assays between the significant points run quite 
uniformly and hence we are justified in assuming that they 
mark the terminals of ore shoots, more especially as the 
character of the ore changes as markedly as the values. 
As we go down the winze the ore changed abruptly, just 
beyond sample 27, from a dark ore, containing copper and 
manganese minerals, into a very white arsenical pryrite. 
Moving along the lower level the ore, although of higher 
grade than the ore just left in the lower part of the winze, 
is still lower than that immediately above it in the top 
level. The character of the ore is also different and hence 
it is in all probability in another ore Shoot. Passing be¬ 
yond cross-course 1 in the lower level we get into ore of 
almost exactly the same character and grade as the ore 
immediately above it in the upper level. Hence we plot 
our ore shoots on the longitu&inal section, as shown by the 
dotted lines in Fig, 8. 

We now turn to the mine records to find out what ore 
pays and what is worthless. We find that $15 covers all 
expenses, but on careful consideration we find that $11 
would do so, if more economical methods of mining were 
introduced. We then find that much of the ore in the block 
under consideration is worthless and must be eliminated 
from our calculations and that practically speaking there 
is only a strip of ore above the lower level and a piece of 
ground, partially stoped, below the upper level. 

My notes show that the ore measures, on the lower 
level, 2.3 feet in width and that it extends fifteen feet 
above the level. It was 340 feet in length. At 12 cubic feet 
to the ton there are 975 tons available for mining, which at 
$28.50 represents $27,787. 

The upper pay shoot is 115 feet in depth and 250 feet 
in length, or 28,750 square feet of stoping ground, of which 
7,200 square feet has been mined, leaving 21,550 square feet. 
The ore is two feet in width or 43,100 cubic feet, or, at 12 
cubic feet per ton, 3,600 tons. At $38.50 per ton the value 
of this pay shoot is $138,600. 

The total amount of ore to be mined is, therefore, in all, 
4,575 tons, worth $166,387. The amount actually recovered 
was about $180,000, of which $40,000, approximately, was 
taken out of new discoveries and from low grade ore which 
had to be mined in carrying out the development work. 
It should, however, be insisted that the block was far too 
large and the cross-courses introduced too many uncer¬ 
tain factors to allow of close approximation, or, at least, 
for the engineer to feel at all certain of the correctness of 



/ 










































ORE IN SIGHT 


43 


























44 


ORE IN SIGHT. 


his deductions. The example is given merely to show how 
much more reliable this method is as compared to the 
slovenly and inaccurate method of averaging the perimeter. 

In a few cases the method which is recommended, by 
inference, by the Institute of Mining and Metallurgy, will 
give approximately the gross value of a mine. It will only, 
however, give the correct tonnage under rare conditions. 
Considered from either the mining or financial standpoint 
it is almost of as much importance to find the tonnage cor¬ 
rectly, or approximately so, as to report the correct value 
of the ore per 'ton. 

The mining of a large amount of low grade ore involves 
very different engineering and metallurgical methods to 
the extraction of a small amount of high grade ore. In 
handling a large body of low grade ore we must consider 
the following items: 

1. —The construction of a large and expensive reduction 
plant. 

2. —The installation of expensive appliances for the 
handling and transportation of material. 

3. —As a very large force of men will be required, ac¬ 
commodations must be provided on a large scale. 

4. —The losses in treatment are generally greater. 

The first three items must be charged against capital 

account, thus, from a financial viewpoint, increasing the 
expense account by additional interest on capital which is, 
of course, charged against the ore. These items may be 
so great that, from the investor’s point of view, the pur¬ 
chase may be a poor one. 

With a smaller tonnage of high grade shipping ore the 
mill question is eliminated, a small force of men is usually 
required, a smaller investment of capital is made in mine 
equipment and the problem is a very different one. 

It is, therefore, of the utmost importance that a mining 
engineer should make an accurate forecast of the amount 
of ore that may be mined as well as the gross value of the 
ore in the mine. This cannot be done by the method of 
averaging the perimeter. 


CHAPTER V. 


From what has been said in the previous chapters we may 
safely conclude that the definition of “ore in sight,” what¬ 
ever that may mean, as being “ore exposed on at least three 
sidto within reasonable distance of each other,” is radically 
wivug. It is fair to state that many of the fatal errors 
made in mining during the past few years can be directly 
traced to this absurd rule. 

As a matter of curiosity the writer attempted to find 
out who was the original author of the rule referred to, 
but without success. It would have been interesting to have 



discovered the reason why the third side was insisted upon, 
l ogically the rule has no foundation. If we wish to measure 
the cubic contents of a block of granite, for instance, it 
would, of course, be necessary to have these dimensions, 
and it is entirely within the limits of presumption to as¬ 
sume that there was some connection between the three 
dimensions of a solid body and the three sides prescribed in 
order that an engineer should be permitted to report on 
available ore reserves. 

There is no logical reason given as to why the sides of 
such a heterogeneous mass as a block of ore should be 
averaged in order to get at the value of the entire block, 
even if it were all of payable value. Is it not obvious that 
the exposed vertical edge of a block, opened on three sides 













46 


ORE IN SIGHT. 


(two levels and an upraise), receives undue weight in the 



Fig. 10. 


calculations? For example in Fig. 9 the shaded portion 
represents a shoot of $20 ore and the unshaded portion $10 
ore. Now if these different shoots are of equal size and 
the edges are of equal length the average of the peiimeter is: 
(15x20x15) -f- 3 = $16.66. 

Whereas the correct value, taking all four sides, is: 
15x20x15x10 ~ 4 $15.00. 

There is only one conceivable case when the average of 
the perimeter will give a correct result, i. e., when all sides 
are of the same value, or approximately so. 

If it were worth while all the illustrations given in this 



a 


c 


c 



















ORE IN SIGHT. 


47 


article could be worked out, showing the falsity of the 
definition of “ore in sight” (available ore reserves) as offi¬ 
cially recognized by the Institute of Mining and Metallurgy, 
and of its corollary the averaging of the values of the 
perimeter. The absurdity of trying to tie the hands of a 
competent miner in his delicate and difficult task of esti¬ 
mating ore reserves and values must be patent to everyone. 
If a man undertakes to do this work he should at least be 
fairly competent to carry it out. If he is not competent 
a few bookish rules can be of no avail. The whole business 
is farcical and is on a par with attempting to prepare rules 
by which doctors are to diagnose sickness. 



In the examination of a block of ground the examiner is 
confronted with these conditions: 

1. In longitudinal section the mass is not homogeneous. 

(a) Some is of high value (shipping ore). 

(b) Another portion is of a milling character. 

(c) Yet other portions are of too low a value to work 
and of this: 

(i) Some may become of value by a small change 
in local conditions; and 

(ii) Much will, under conceivable conditions, 
never become valuable. 

(2) Seen in transverse section, i. e., from wall to wall, 
the deposit, if a fissure vein, is built up of layers which may 
be classified as above. 

It must be clear that all these conditions must be ascer¬ 
tained with a close approximation to accuracy before any 
calculations can be made as to available ore reserves and 
the value of the block from a speculative point of view. 








48 


ORE IN SIGHT. 


Each block may therefore require a number of distinct 
sets of calculations in order that the following facts can 
be arrived at: 

(1) The tonnage of high grade, or shipping, ore and its 
value. 

(2) The tonnage of milling ore and its value. 

(3) The tonnage and value of ore which may become 
available: 

(a) By the reduction in working charges of $1 per ton. 

(b) By the reduction in working charges of $2 per ton. 

(c) By the reduction in working charges of $3 per ton. 

Etc., etc. 

An underpaid and overworked engineer may be pardoned 
if he arrives at the third item by rapid approximate meth¬ 
ods, but if his work does not show with reasonable accuracy 
the first two his work is unminerlike and unprofessional. 
It might be urged against this statement that the examina¬ 
tion of ore deposits would become very difficult and com¬ 
plex. In answer to this it can be justly said that no man 
who cannot unravel a fairly simple problem such as this 
should undertake the examination of a mine and label his 
results as the value of “ore in sight.” An expert account¬ 
ant has to unravel much worse problems than the one indi¬ 
cated above. 



Let us first examine the variations shown in longitudinal 
section. We cannot hope to mention all the combinations 
possible, but at least five are common and readily recog¬ 
nized. 

In Fig. 1 is shown a block in which the ore is partially 










ORE IN SIGHT. 


49’ 


pay and partially below pay. In running a line of samples 
from B to B' examination of the assay records shows that 
the ore has certain characteristics and has no commercial 
value. From B' to A the ore is good, from A to D likewise 
and from D to C' also. In this part of the block the ore is 
of very similar character and doubtless belongs to the same 
Oie shoot. From C' to C the ore is similar in character and 
value to that from B to B'. In calculating the value of this 
block of ground the portion B B' C C' is eliminated and 
only B' A D C' is estimated on as “ore available for stop- 
ing.” 

in averaging the perimeter in Fig. 10 there are chances 
that the whole block may fall below pay and the rule so 
often referred to may cause the rejection of the entire mass. 
If, however, the shaded portion carried good values that 
part alone must be estimated and a fair profit may be made. 
The localization of the shoot is performed as in the preced¬ 
ing example (Fig, 9). 

Now in Fig. 11 we have an example of an ore shoot com¬ 
ing down fiom the block above and shown at A' B', but of 
which no evidence can be found on the level D C. It there¬ 
fore terminates somewhere in the interior of the block. The 
remainder of the block may be of fair pay value, and if the 
perimeter be averaged it can be shown that the assumption 
is that the high grade shoot terminates half way down or 
at about X; but it may terminate at W, Y or Z. In these 
latter cases the estimate will be in error. It is wiser, there¬ 
fore, to eliminate from the calculation the area A', B', C', D', 
and calculate the value of the remainder of the block. The 
area eliminated should be transferred to the class com¬ 
monly called “problematical” or speculative ore. A maxi- 
m.um and a minimum value should be indicated for such ore. 

In Fig. 12 we have a block of ground where the ore shows 
a distinct change in character and value at the point E in 
the upraise. In such a case the block is insufficiently de¬ 
veloped unless the side B, C, is opened up. If valued in 
the ordinary way it would be assumed that the block con¬ 
sists of two distinct parts A B E F and E D C F, with the 
line of contact running from E to F, But it is conceivable 
that the line of contact may be E C or E B or anywhere 
between B and C. Still, the engineer must, or should, in¬ 
dicate the possible values of such a block of ground, espe¬ 
cially if it contains ore which assays well. Only problem¬ 
atical values can be assigned, with a maximum, minimum 
and a mean. The fourth side should have been opened. 

In the Fig. 13 we have a case in which only two of the 


50 


ORE rx SIGHT. 


three sides opened show good ore. This is one which is apt 
to give the greatest error by the method of averaging the 
perimeter, for the high assays in the block are counted in 
on two sides and the low assays in one, whereas the areas 
of high and low grade ore may be equal. Let us, however, 
assume that the sides B C and C D are the high grade 
edges and that A B shows ore of no commercial value. It 
must be obvious that a change takes place within the block 
somewhere. But where? Is the line of contact from B to D 
or does it run from B to a? If from B to a an underestima¬ 
tion is made if a triangular block, B C D, of pay ore is 
assumed. As a matter of fact the block is insufficiently de¬ 
veloped and should not be classed with ore available for 
stoping. 

We thus see that there are cases where, as in Fig. 2 two 
sides only may expose ore sufficiently to allow measurement 
and calculation of ore values; in other cases three sides are 
insufficient. In all cases the average of the perimeter 
could not have given correct valuation. 


CHAPTER VI. 


In the preceding chapter attention was directed to the fact 



that not only was a block of ore very heteregeneous, when 
seen in longitudinal section, but also when seen in cross 
section—that is, from wall to wall of the vein. Let us take 
a characteristic example as in Fig. 14. Here we have the 
breast of a drift showing three distinct layers or “streaks” 
of ore of different grades, as well as “vein filling” or gan- 
gue. A careful examiner would endeavor to size up the 
situation so as to indicate to the prospective purchaser: 

(1) How much ore would be high enough in value to 
ship without milling or other treatment, except, possibly, 
hand picking; and 


















52 


ORE IN SIGHT 


€ 




t 



ir> 


' rs'* a> 
[.«*/ •— 
Ul 


» 


Section of a Thin Vein Exposed in a Level. 

































Fig. 16—Section of a Thick Vein, 


•i 

ORE IN SIGHT. 


53 














































54 


ORE IN SIGHT. 


(2) The value and tonnage of mill ore. 

(3) The amount of ore of doubtful value. 

In the example given we cannot hope to show the real 
condition of affairs by a simple longitudinal section, for 
such a section can only represent one streak or the average 
value of them all. Either representation is invalid for the 
sufficient reason that, when the streaks are wide enough 
any miner worth his salt will practically mine each streak 
separately. Each product would be sent to the surface 
separately and all that could be left standing would not be 
broken down. 

The only method which can give satisfactory results is 
to draw each block in isometric projection. This method is 
simple, is drawn to scale and allows the condition of affairs 
to be shown clearly and with a close approximation to ac¬ 
curacy. It may, however, be necessary in many cases to 
plot the conditions on each level, upraise or winze to scale 
for the sampling record. 

In that admirable paper on “Sampling and Measurement 
of Ore Bodies,” by E. B. Kirby,* the mmthod was shown in 
full detail. As the paper is not as well known as it should 
be and as the drawings illustrate just what the present 
writer means they are reproduced with the necessary de¬ 
scriptions written by Mr. Kirby. 

Fig. 15 shows the plan of an ordinary thin vein presented 
in a level when the entire width is exposed. It is self-ex¬ 
planatory. 

Fig. 16 shows a thick vein which is exposed by cross cuts 
and the drift. This is explained by Mr. Kirby thus: 

The limit abed may be taken if the entire mass is 
pay ore, but if it is limited to a few streaks like the two 
shown, their continuance is less certain and a b f d is taken. 

These sections can be readily used in making isometric 
projections as in the following examples, Figs. 17 and 18: 

“In the simple case illustrated by Fig. 17 the pay area in 
each section is converted to an equivalent trapezoid like 
abed, whose shape conforms as closely as possible to the 
average actual shape of the pay streak by having the same 
length and by being wider at one end than the other, if 
necessary. The ends a b and c d are parallel. The two 
trapezoids are sides of an irregular wedge to which the pris- 
moidal formula is applied.” 

These illustrations are typical of the manner in which 
the ore bodies should be traced and represented. They are. 


*Colo. Sci. Soc., Dec., 1895. 



ORE IN SIGHT. 


55 


in fact, picture models of the manner in which the values 
are distributed through the deposit. They allow the engi¬ 
neer to calculate the ore values with a close degre of ac¬ 



curacy and more important yet, allows him to foreshadow 
the possible prospective value of the property, for he can 
get an excellent idea of the trend of ore shoots and the 
probability of finding new ores. The absurd rule of the 
three sides gives no such information and without the as¬ 
sistance of such diagrams the examining engineer has to 
rely upon that notoriously weak reed, unaided “judgment.” 



In valuing an ore deposit it is absolutely essential that 
not only should the mine be thoroughly developed, but it is 
essential that a light method be adopted for the examina¬ 
tion. In order, therefore, for an engineer to be able to 
report ore available for stoping, “ore in sight,” he must 

























56 


ORE IN SIGHT. 


have: (1) A correct method of sampling; and (2) sufficient 
development work. Each is useless without the other and 
each is equally as important. No rule can be given as to 
when ore is or is not in sight without giving as a corollary 
that the method of sampling should be adapted to the par¬ 
ticular deposit under examination. 

The question of mine sampling is so involved that its 
consideration must be left to a future occasion. It is hoped, 
however, that the writer has assisted in burying one of the 
most absurd rules that ever hampered the work of the 
mining engineer. 


CHAPTER VII. 


In estimating the value of a mine it is hardly necessary 
to state that the value of the available ore, as found by 
measurements and sampling, is merely one of the factors 
involved. There is always a certain tonnage of ore which 
is of too low a value to warrant mining under present con¬ 
ditions. For example, in an examination the engineer may 
find that there may be some thousands, or even hundreds 
of thousands, of tons of ore which, if mined and treated, 
would involve a heavy financial loss. 

It has been frequently stated by men whose opinions 
are worth consideration that no large body of ore bearing 
material can ever be permanently kept out of the market. 
That changes in conditions may, at some future time, ren¬ 
der such masses of considerable commercial value. Time 
and a judicious expenditure of money in large scale en¬ 
gineering work may cause what is now valueless material 
to become of importance to the miner. It is only necessary 
to allude to the zinc ores of Leadville as an illustration of 
such a case. 

It is but a few years since that the zinc ores of Colorado 
were the bane of the miner. They had no intrinsic value, 
but on the contrary the presence of zinc in the lead-iron- 
silver ores caused such high “penalties" that they could 
not be mined and smelted at a profit. The advent of the 
magnetic concentration process and the growing demand 
for zinc white pigments has changed all that, and instead 
of the ores being a bane they now add considerably to the 
annual value of the minerals raised in Colorado. 

In the valuation of a mine, therefore, it is necessary to 
take into consideration the possible value of much material 
that is not immediately available. If, for example, a mine 
has $1,000,000 worth of immediately available ore opened 
up and $1,500,000 is asked for it, the question of whether 
the property is a good purchase or not seems a dubious one. 
The answering of this question involves two considerations 
at least. First, is there much virgin ground to be devel¬ 
oped, and if so, are the prospects such as to warrant ex¬ 
pectation that large bodies of ore will be opened up? 
Secondly, what possibilities are there of reducing the cost 
of mining, milling and general supplies to such a point that 



58 


ORE IN SIGHT. 


ore, which now cannot be mined, can be made available? 
In this latter case, of course, the increased value of the ore 
which is sin'ely available has to be considered. 

Ill considering the latter problem the tabulation of the 
grades of the ore according to the net losses becomes of 
great value. For example, the engineer finds that in a 
number of different places in the mine there are several 
thousands of tons of ore which, if mined, would entail a 
loss of $1.00 per ton; in other places so many more thou¬ 
sands which would entail a loss of $2.00 per ton, and so 
on down. 

By bringing in a good water supply, by decreasing the 
cost of fuel and mine timber, by better milling facilities 
and so forth the charges against the ore may be reduced 
by several dollars to the ton. Many thousands of tons of 
ore are then brought within the scope of practicable min¬ 
ing. It necessarily follows that the cost of making the 
improvements must not be in excess of the value of the 
ore which is to be made available. If this condition is ful¬ 
filled it must be apparent that the ore alluded to forms a 
valuable asset often sufficient, indeed, to warrant the price 
asked for the mine. 

Good mining engineering will doubtless solve many such 
problems as those considered, and to-day many of the most 
desirable investments are of this character. In reporting 
on “possibilities,” therefore, the examining engineer is 
bound to consider not only the amount of ore which may 
possibly be opened up in new ground, or which is not suffi¬ 
ciently developed as to warrant it being placed in the class 
of “available” ore, but that ore which by careful manage¬ 
ment and good engineering is brought within the zone of 
practicable mining. 




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